Method and Circuit for Accessing RFID Tag

ABSTRACT

A radio frequency identification (RFID) tag access method and a circuit applied to an RFID tag to determine whether to respond to a command sent by a reader are provided. According to the access method, an extra reference value is used for adjusting a parameter or a count value, so as to increase or decrease the probability of generating a condition matching with a command sent by the reader. Therefore, the probability of the tag being accessed is adjusted, and the tag carrying urgent information shall be accessed prior to the tag without urgent information.

CROSS REFERENCE TO RELATED PATENT APPLICATION

This patent application is based on a Taiwan, R.O.C. patent applicationNo. 97135963 filed on Sep. 19, 2008.

FIELD OF THE INVENTION

The present invention relates to a radio frequency identification (RFID)technology, and more particularly, to an RFID technology of adjustingthe probability of a tag being accessed.

BACKGROUND OF THE INVENTION

A conventional RFID system is illustrated in FIG. 1. The RFID system 100comprises tags 110, a reader 120, radio frequency (RF) antennas 130, anda host 140 for processing identification signals. Non-contact datatransmission between the tag 110 and the reader 120 is achieved by usingRF signals. A communication protocol, for an example, the electronicproduct code (EPC) is a common transmission specification of suchnon-contact data transmission. In the communication protocol of the EPC,the reader 120 finds every tag 110 within a certain range and accessescontent of the tags 110 according to a Q-algorithm or an anti-collisionsearching method. The reader 120 generates a Q value, and sends a querycommand having the Q value to every tag 110 within the range. The tag110 randomly generates a count value according to the Q value whenreceiving the query command. Provided that when the generated countvalue is equal to 0, the tags 110 will then respond to the query commandof the reader 120; and when only one of the tags 110 is responsive, thereader 120 transmits data to such tag 110. However, when more than oneof the tags 110 simultaneously respond to the query command of thereader 120, the reader 120 again sends a command for resetting the Qvalue until that a count value of only one of the tags 110 is equal to0.

In the foregoing Q-algorithm, as a result of all of the tags 110 havinga same Q value and a same random procedure, the probability of randomlygenerating the count value of zero is the same. In other words, theprobability of every tag 110 being accessed is the same. However, whenthere is one particular tag 110 carrying urgent information which needsto be accessed with a higher priority, the conventional Q-algorithm cannot ensure that this tag 110 is accessed as quickly as possible.

SUMMARY OF THE INVENTION

One objective of the present invention is to provide an RFID technologyof adjusting the probability of an RFID tag being accessed. A tagcarrying urgent information is accessed prior to a tag without urgentinformation, so as to solve the problems in the prior art.

According to an embodiment of the present invention, an RFID tag accessmethod is provided. The access method comprises steps of storing aparameter and a first reference value in a tag, generating a count rangeaccording to the first reference value, selecting a count value withinthe count range, and determining whether the tag should respond to acommand sent by a reader according to the count value.

According to another embodiment of the present invention, an RFID tagaccess method is provided. The access method comprises steps of storinga parameter and a reference value in a tag, generating a count rangeaccording to the parameter, selecting a count value within the countrange, subtracting the reference value from the count value to generatean adjusted count value, and determining whether the tag should respondto a command sent by a reader according to the adjusted count value.

Moreover, according to an embodiment of the present invention, an accesscircuit, applied to an RFID tag, for determining whether to respond to acommand sent by a reader, is disclosed. The circuit comprises a memory,a count value generating circuit, and a controlling circuit. The memorystores a parameter and a first reference. The count value generatingcircuit generates a count range according to the first reference value,and selects a count value within the count range. The controllingcircuit then determines whether the RFID tag should respond to thecommand according to the count value.

Furthermore, according to another embodiment of the present invention,an access circuit, applied to an RFID tag, for determining whether torespond to a command sent by a reader, is disclosed. The access circuitcomprises a memory, a count value generating circuit, and a controllingcircuit. The memory stores a parameter and a reference value. The countgenerating circuit generates a count range according to the parameter,selects a first count value within the count range, and subtracts thereference value from the first count value to generate a second countvalue. The controlling circuit then determines whether the RFID tagshould respond to the command according to the count value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a conventional RFID system.

FIG. 2 is a schematic diagram of an access circuit applied to a RFIDsystem according to an embodiment of the present invention.

FIG. 3 is flow chart of an access method according to an embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An RFID tag access method according to the present invention can adjustthe probability of an RFID tag being accessed. In the method, at least areference value is used for adjusting a Q value or a count value. FIG. 2is a schematic diagram of an access circuit applied to an RFID tag, andthe circuit is used for determining whether to respond to a command sentby a reader, such as a reader 120 of an RFID system illustrated inFIG. 1. Referring to FIG. 2, the circuit comprises a memory 210, a countvalue generating circuit 220, and a controlling circuit 230. The countvalue generating circuit 220 further comprises an adjusting circuit 222and a calculating circuit 224. The memory 210 stores a Q value, a countvalue, and at least one reference value, such as a first reference valueR1 and a second reference value R2 according to an embodimentillustrated in FIG. 2. The Q value is a parameter which is set via acommand sent by the reader, and the reference value is either builtinside the memory 210 or is set via the command sent by the reader.

In a first embodiment of the present invention, the adjusting circuit222 adjusts the Q value set by the reader according to the firstreference value R1, and the calculating circuit 224 generates a countrange according to the adjusted Q value. When a count value is selectedfrom the count range by the calculating circuit 224, the controllingcircuit 230 determines whether to respond to the command of the readeraccording to the count value. In a second embodiment, the calculatingcircuit 224 generates a count range according to the Q value, andselects a count value from the count range. The adjusting circuit 222then subtracts the second reference value R2 from the count value togenerate an adjusted count value. Then, the controlling circuit 230determines whether to respond to the reader according to the adjustedcount value. In addition, a third embodiment is rendered by combiningthe first embodiment and the second embodiment. The adjusting circuit222 adjusts the Q value set by the reader according to the firstreference value R1, and the calculating circuit 224 generates a countrange according to the adjusted Q value. When a count value is selectedfrom the count range, the adjusting circuit 222 further subtracts thesecond reference value R2 from the count value to generate an adjustedcount value. In the foregoing embodiments, the count range or the countvalue is controlled by way of selecting the first and the secondreference values or selecting the adjusting methods of the adjustingcircuit 222. Hence, the probability of the count value being equal to 0can be increased or decreased to adjust the probability of a tag 200being accessed.

The foregoing embodiment is illustrated in conjunction with a flowchart.Noted that under a premise that the same effect is achieved in practice,the steps of generating the count value by the tag 200 need not beexecuted as the sequence shown in FIG. 3. The steps in FIG. 3 can beinterleaved with other steps of the same flow.

Referring to FIG. 3, the flow that the tag 200 determines whether torespond to a command sent by a reader comprises steps below.

In Step 310, a setting command sent by the reader is received. Thesetting command comprises a first reference value R1, a second referencevalue R2, and a function enabling parameter. The function enablingparameter indicates whether the tag 200 uses the first reference valueR1 or the second reference value R2 for adjusting a Q value or a countvalue. For example, when the function enabling parameter is equal to 1,an adjust function of the adjusting circuit 222 within the tag 200 isstarted; when the function enabling parameter is equal to 0, the adjustfunction of the adjusting circuit 222 within the tag 200 is shut down,and the tag 200 implements a conventional Q-algorithm to generate thecount value. Moreover, as described above, the first reference and thesecond reference values are set in the memory 210 in advance, and atthis point the predetermined first and second reference values may notbe contained in the setting command.

Generally speaking, since the setting command comprises parameters, suchas the function starting parameter, the first reference value R1, andthe second reference value R2, a conventional tag, which doesn't havethe adjusting function, cannot identify these parameters. As a result,in order to avoid influencing statuses of other conventional tags andany potential errors, the reader sends the setting command beforeperforming any RFID tag query command.

In Step 315, the tag 200 sets the function enabling parameter, the firstreference value R1, and the second reference value R2 in the memory 210according to the setting command. As mentioned above, the firstreference value R1 and the second reference value R2 can also be set inthe memory 210 in advance. In an embodiment, the function enablingparameter of the tag 200 is reset via the command of the reader afterall tags within a range are accessed.

In Step 320, the tag 200 receives a query command sent by the reader.

In Step 325, the tag 200 determines the type of the query commandreceived, such as a query, a query rep and a query adjust illustrated inFIG. 3. When the query command indicates that the tag 200 begins thequery, a first responding procedure 326 is executed so that the tag 200generates a count value randomly. When the query command indicatesrepeating the query, a second responding procedure 350 is executed sothat the tag 200 adjusts the original count value. When the querycommand indicates an query adjustment, a third responding procedure 328is executed so that the tag 200 generates a count value again accordingto the adjusted Q value.

The first responding procedure 326 comprises Step 330 to Step 334. InStep 330, when the query is executed, the adjusting circuit 222 replacesthe Q value in the query command with the first reference value R1. InStep 332, the calculating circuit 224 further generates a count rangeaccording to the adjusted Q value, i.e., the first reference value R1.In an embodiment, the count range is from 0 to 2^(m)−1, where m is thefirst reference value R1. In Step 334, the calculating circuit 224selects a number from the count range as the count value of the tag 200,and stores the count value in the memory 210. In an embodiment, thecalculating circuit 224 randomly selects the count value from the countrange.

In Step 340, the controlling circuit 230 determines whether the countvalue is equal to or smaller than 0. When the count value is equal to orsmaller than 0, Step 345 of responding to the query command of thereader is executed. Otherwise, Step 320 of receiving a query command isrepeated.

In Step 345, the tag 200 enters a reply state after responding to thequery command of the reader, and sends an EPC of the tag 200 to thereader after responding to an EPC acknowledge (ACK) command of thereader.

Therefore, in the first responding procedure 326, in order to increasethe probability of the tag 200 being accessed, the first reference valueR1 is set as being smaller than the Q value to narrow down the countrange, and the probability of the number of 0 being randomly selected isfurther increased. In an embodiment, the Q value is directly replacedwith 0 in Step 330. Hence, the number of 2^(m)−1 generated in Step 332is 0 and the count value selected in Step 334 is definitely equal to 0.On the contrary, in order to make the tag 200 be accessed later, thefirst reference is set as being greater than the Q value to enlarge thecount range, so as to decrease the probability of the count value beingequal to 0.

The second responding procedure comprises Step 350. In Step 350, whenthe query command indicates repeating the query, the adjusting circuit222 subtracts the second reference value R2 from the count value storedin the memory 210 to generate the adjusted count value, which is storedinto the memory 210. When the adjusted cont value is equal to or smallerthan 0, the tag 200 responds to the query command of the reader. It isto be noted that, the second reference value R2 is equal to or greaterthan 1, so as to quickly converge the count value to be equal to orsmaller than 0.

The third procedure 328 comprises Step 360 to Step 369, which areillustrated as below.

In Step 360, when the query command indicates adjusting the query, theoperation of either increasing or decreasing the Q value is performed.For example, when the tags responding to the query command areredundant, the reader increases the Q value; when the query command isunable to get a response, the reader decreases the Q value. When the Qvalue is increased, Step 362 of correspondingly adding 1 to the Q valueis executed; otherwise, Step 364 of correspondingly subtracting 1 fromthe Q value is executed.

In Step 366, the adjusting circuit 222 adjusts the Q value according tothe first reference value R1.

In Step 368, the calculating circuit 224 generates a count rangeaccording to the adjusted Q value. In an embodiment, the count range isfrom 0 to 2^(Q′)−1, where Q′ is the adjusted Q value.

In Step 369, the calculating circuit 224 selects a number from the countrange as the count value of the tag 200, and stores the selected countvalue in the memory 210. In an embodiment, the calculating circuit 224randomly selects the count value from the count range. When the countvalue is equal to or smaller than 0, the tag 200 responds to the querycommand of the reader.

In an embodiment, the adjusting circuit 222 in Step 366 divides the Qvalue by a function of the first reference value R1, such as 2^(m),where m is the first reference value R1. As a result, an adjusted Qvalue smaller than Q value is generated to narrow down the count rangegenerated in Step 368 and to further increase the probability of thecount value generated in Step 369 being equal to 0, so that the tag 200is accessed with high priority. In another embodiment, the adjustingcircuit 222 multiplies the Q value by a function of the first referencevalue R1 to enlarge the count range and to decrease the probability ofthe selected count value being equal to 0, so that the probability ofthe tag 200 being accessed is decreased.

In conclusion, in an access flow 300, an extra reference value is usedfor adjusting the Q value or the count value, so as to increase ordecrease the probability of generating a condition matching with acommand sent by the reader. For example, the condition is that the countvalue is equal to or smaller than 0. Therefore, the probability of thetag being accessed is adjusted, whereby the tag carrying urgentinformation is accessed prior to the tag without urgent information.

Frequency segments of the RFID system are generally classified as a lowfrequency segment covering from 0 kHz to 300 kHz, a high frequency (HF)segment covering from 3 MHz to 30 MHz, an ultra high frequency (UHF)segment covering from 300 MHz to 960 MHz, and a microwave frequencysegment covering from 2.45 GHz to 1000 GHz. Application fields, accessdistances or prices of different frequency segments are respectivelydifferent. The tag 200 and the reader according to the foregoingembodiments comply with an EPC generation 2 specification of an RFIDsystem operating in UHF or HE The RFID system, complying with the EPCgeneration 2 specification, having a large storage volume for storingtag information and being highly accurate, is generally applied tovarious tags, chips, printers and coders.

While the invention has been described in terms of what is presentlyconsidered to be the most practical and preferred embodiments, it is tobe understood that the invention needs not to be limited to the aboveembodiments. On the contrary, it is intended to cover variousmodifications and similar arrangements included within the spirit andscope of the appended claims which are to be accorded with the broadestinterpretation so as to encompass all such modifications and similarstructures.

1. A radio frequency identification (RFID) tag access method comprisingsteps of: storing a first parameter and a first reference value in anRFID tag; generating a count range according to the first referencevalue; selecting a count value within the count range; and determiningwhether the RFID tag responds to a query command sent by a readeraccording to the count value.
 2. The access method as claimed in claim 1further comprising a step of: receiving a setting command sent by thereader, wherein the setting command comprises the first reference value.3. The access method as claimed in claim 2, wherein the setting commandfurther comprises a function enabling parameter for indicating whetherthe RFID tag uses the first reference value.
 4. The access method asclaimed in claim 2, wherein the reader sends the setting command beforeperforming the query command.
 5. The access method as claimed in claim2, wherein the step of generating the count range according to the firstreference value comprises: adjusting the first parameter according tothe first reference value to generate a second parameter; and generatingthe count range according to the second parameter.
 6. The access methodas claimed in claim 5, wherein the step of adjusting the first parameteraccording to the first reference value comprises replacing the firstparameter with the first reference value.
 7. The access method asclaimed in claim 5, wherein the step of adjusting the first parameteraccording to the first reference value comprises calculating the firstparameter with the reference value to generate the second parameterwherein the second parameter is smaller than the first parameter.
 8. Theaccess method as claimed in claim 1, the step of storing the firstparameter and the first reference value in the RFID tag furthercomprising storing a second reference value which is equal to or greaterthan 1, the access method further comprising: subtracting the secondreference value from the count value.
 9. The access method as claimed inclaim 1, wherein the RFID tag is in compliance with a generation 2specification of an electronic product code operating in ultra highfrequency or high frequency.
 10. An RFID tag access method, comprisingsteps of: storing a parameter and a reference value in an RFID tag,wherein the reference value is equal to or greater than 1; generating acount range according to the parameter; selecting a first count valuewithin the count range; subtracting the reference value from the firstcount value to generate a second count value; and determining whetherthe RFID tag responds to a query command sent by a reader according tothe second count value.
 11. The access method as claimed in claim 10further comprising a step of: receiving a setting command sent by thereader, wherein the setting command comprises the reference value. 12.The access method as claimed in claim 10, wherein the RFID tag is incompliance with a generation 2 specification of an electronic productcode operating in ultra high frequency or high frequency.
 13. An accesscircuit, applied to an RFID tag, the circuit comprising: a memory, forstoring a first parameter and a first reference value; a count valuegenerating circuit, for generating a count range according to the firstreference value and the first parameter, and selecting a count valuewithin the count range; and a controlling circuit, for determiningwhether the RFID tag responds to a query command sent by a readeraccording to the count value.
 14. The access circuit as claimed in claim13, wherein the reader sends a setting command having the firstreference value to be set into the RFID tag.
 15. The access circuit asclaimed in claim 14, wherein the setting command further comprises afunction enabling parameter for indicating whether the count valuegenerating circuit uses the first reference value.
 16. The accesscircuit as claimed in claim 14, wherein the reader sends the settingcommand before performing the query command.
 17. The access circuit asclaimed in claim 13, wherein the count value generating circuitcomprises: an adjusting circuit, for adjusting the first parameter togenerate a second parameter according to the first reference value; anda calculating circuit, for generating the count range according to thesecond parameter.
 18. The access circuit as claimed in claim 17, whereinthe adjusting circuit replaces the first parameter with the firstreference value.
 19. The access circuit as claimed in claim 17, whereinthe adjusting circuit calculates the first parameter according to thefirst reference value to generate the second parameter wherein thesecond parameter is smaller than the first parameter.
 20. The accesscircuit as claimed in claimed 13, wherein the memory further stores asecond reference value which is equal to or greater than 1, and thecount value generating circuit subtracts the second reference value fromthe count value.
 21. An access circuit, applied to an RFID tag, thecircuit comprising: a memory, for storing a parameter and a referencevalue; a count value generating circuit, for generating a count rangeaccording to the parameter, selecting a first count value within thecount range, and subtracting the reference value from the first countvalue to generate a second count value; and a controlling circuit, fordetermining whether the RFID tag responds to a command sent by a readeraccording to the second count value.
 22. The circuit as claimed in claim21, wherein the reader sends a setting command having the referencevalue to be set into the RFID tag.